"It could have been worse," he said, "there were over 200 men working onsite and another 150 at the primary school, including one guy working on the roof.

"So you get a sense of the potential size of the tragedy."

Key said houses in the cordon fit the bill of those struck by tornadoes in America.

"I can say I have never seen anything like this in New Zealand before," he said. "It's far more significant than a very bad storm where you have a few trees down.

"It's something you would expect to see in mid-west America not in Hobsonville."

Key said there were 150 damaged homes, many of which are so badly damaged they are beyond repair.

"I understand 115 of those were Defence Force owned and 35 were rented out," he said. "I would say a certain number of houses will be uninhabitable.

"Many were slated to be demolished so they weren't in the best of condition anyway."

Key said Auckland Council will work to find accommodation for people with no place to live.

The council is still looking after a number of lost animals at the West Auckland Animal Shelter.

The Ministry of Social Development has activated the Government helpline for people who require information about services and assistance.

The helpline number is 0800 779 997.

DIED SHELTERING FROM STORM

The three victims of yesterday's tornado died when they were crushed by a falling concrete slab on the Hobsonville High School construction site, while they sheltered in a truck.

The health and safety team from the Ministry of Business Innovation and Employment (MBIE) was investigating the tragedy.

Emergency services experienced more than a 150 per cent increase in calls in the first half hour after the tornado hit, Telecom has revealed.

Spokeswoman Jo Jalfon said that translated to about 100 calls between 12.25 and 12.45pm yesterday.

She said at one point, calls peaked to 212 per cent of normal call volumes.

"The majority were for Fire Service, so were to do with flooding and damage and things like that."

Emergency services were only expecting about a 70 per cent increase in volume for the storm.

STORM CAUSES $11M DAMAGE

Civil Defence says the damage inflicted would cost $11 million to repair.

A total of 230 people had their homes damaged or destroyed, and many have been accommodated at the Whenuapai Air Force base.

Two recovery centres opened this morning with agency staff onsite to help those displaced.

Waitemata Police District Commander Superintendent Bill Searle said Civil Defence staff were working as quickly as possible to establish which houses in the affected area of Hobsonville were safe for their owners to return.

"In the meantime I ask everyone to be patient, " he said.

About 570 people were still without power this afternoon and some areas, including Waimarie and Totara roads, were not expected to have power until Sunday.

Lines company Vector has told people not to use generators to power applicances in their homes.

Auckland Council is looking after misplaced animals at its West Auckland animal shelter at 48 The Concourse.

The council is also responding to requests to fix damaged stormwater systems throughout Auckland.

BREAKFAST BEHIND THE CORDON

True community spirit is coming out in Hobsonville as residents put others ahead of themselves.

A number of residents were today living in the damage zone behind a tightly-guarded cordon, which has since been lifted.

Bread, milk and the essentials are banned for those who stayed behind.

Desiree Morgan and her two daughters were desperate for breakfast this morning, but going to the dairy up the road meant deserting their undamaged house.

"We don't want to go out because then we can't go back," the mother said.

"The cops told us if you leave you can't go back."

But getting milk across the cordon was easy for an unnamed woman who couldn't bear to see Morgan's children go without breakfast.

"I've had two hours of sleep, it's too much truly," she said before running away from congratulating neighbours and disapproving police.

GUSTS MOST DAMAGING

While the tornado in Auckland packed winds of more than 200kmh, some of the most damaging winds were the "striaght gusts" which came immediately before and after the mini twister, MetService said.

Meteorologist Dan Corbett said straight-line gusts of up to 110km were what caused considerable damage out at Whenuapai.

"The mini tornado obviously does some serious damage but they also have the potential to kick out some serious winds as they release."

He said a "cold upper pool" was hovering over parts of the North Island today giving moderate risk of thunderstorms particularly in the North Island, particularly from Waikato down.

"We can't rule out the risk of tornadoes in those areas," he said.

Wellington was also at risk of thunderstorms in the afternoon, although no tornado risk was presumed for the capital - just heavy hail.

The tornado inflicted at least $11 million of damage, civil defence says.

A North Shore Hospital spokeswoman said only one patient had been kept in overnight. The woman had suffered a fractured pelvis during the tornado.

She was in a comfortable condition.

Power supply company Vector says around 1300 homes lost their power in the storm, and a lightning strike in Piha, and by this morning 635 homes, mainly in the storm area, were still without electricity.

The company says they will not be restored until authorities check that the damaged homes remain safe.

LINE OF THUNDERSTORMS

Auckland and a swathe of the North Island which included Rotorua and Gisborne were hit yesterday afternoon by an intense line of thunderstorms and heavy rains.

Another tornado touched down near Rotorua without injuries.

The worst damage was inflicted near the Whenuapai air force base and on nearby Hobsonville, a former air force base now being transformed into a large housing estate.

Most of the damage was done to Defence Force housing.

Defence Force staff and civilians accommodated at Whenuapai Air Force base showed a variety of emotions, Group Captain Kevin McEvoy told Radio New Zealand.

"Obviously they are happy to at least be safe, but some of them have obviously lost their houses and belongings," he said.

The response to the tornado was a major coordinated activity, he said.

"New Zealand police have got the lead, but we've been supporting them throughout the night; St John, Civil Defence, Auckland City Council, Red Cross, and the list goes on."

DISASTER RESPONSE 'OUTSTANDING'

Auckland mayor Len Brown said the response to the disaster by authorities was outstanding.

"We have learnt a lot from Christchurch," he told Radio New Zealand.

The response had huge pace and momentum.

"The community would have felt absolutely embraced and supported," Brown said.

He appealed for people to stay away from the area today unless they could help, and he asked that the families of the dead be respected.

"I am very focussed on the families, there have been three bereavements and three men did not come home last night."

Brown said the residents had been hugely traumatised.

The storm had gone through the area several times: "It had gone around it like the tub of the washing machine."

Brown said he would spend the day talking to residents in the area.

VICTIM 'LIFE OF THE CONSTRUCTION SITE'

The fatalities happened at the site where a new school is being built.

Contractors were working on the new high school when 15-metre high concrete tilt-slab walls were picked up by the storm and slammed into sheltering workers.

"There was about two or three of them that tipped over and a couple landed on the truck and one landed half on the ground and half on the truck,'' plumber Sam Nuthall said.

"That was the one that landed on top of the two guys.''

The three men killed were in the truck or beside it.

One of the men killed had been ''the life of the construction site'' he said.

He said he had a bit of a laugh with the man, he named as Tom [Stowers].

Nuthall said he'd been nagging Tom to move a support brace so that he could move his digger and they ''had a bit of a chuckle about that''.

Rescuers needed a large crane to remove the concrete and it wasn't until early last night that the bodies were recovered.

The tornado inflicted damage along around a kilometre of Wallingford Way - named after Sidney Wallingford, one of the founding pilots of the air force - where 220 homes were declared uninhabitable.

- Earlier it was reported that a Department of Labour (MBIE) spokeswoman said the department was not involved as it appeared to be an ''act of God''. This has been corrected.